The overall objective is to define more precisely how various factors affect the patterns of particle deposition which occur during inhalation. Specifically we propose: 1) to investigate how gravity and pleural pressure gradients influence alveolar deposition. By analyzing small samples of dried or frozen lungs, we plan to measure the amount of alveolar deposition in different lung regions. We also plan 2) to investigate how the various breathing patterns influence the distribution of particle deposition. A servo-pressure control system will be used to produce any desired breathing pattern at any specified lung volume. Finally, we plan 3) to investigate species differences with regard to aerosol deposition and to attempt to apply principles of scaling to our experimental data with the goal of developing predictive powers. Since inhalation is the primary entry route for agents that environmental, occupational, and infectious disease, it is clearly important to understand better how and where particles deposit in the lungs. The information will be of value in understanding and controlling environmental hazards.